Urinary tract infection caused by a small colony variant form of capnophilic Escherichia coli leading to misidentification and non-reactions in antimicrobial susceptibility tests

BackgroundSmall colony and capnophilic variant cases have been separately reported, but there has been no reports of their simultaneous presence in one isolate. We report a case of Escherichia coli with coexpressed small colony and capnophilic phenotypes causing misidentification in automated biochemical kits and non-reactions in antimicrobial susceptibility test cards.Case presentationAn 86-year-old woman developed urinary tract infection from a strain of Escherichia coli with SCV and capnophilic phenotypes in co-existence. This strain did not grow without the presence of CO2, and therefore proper identification from automated system was not possible. 16s rRNA sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was able to identify the bacteria.ConclusionAs these strains do not grow on culture parameters defined by CLSI or on automated systems, proper identification using alternative methods are necessary.